1. Field of the Invention
The present invention relates to an apparatus for producing cased coil springs for use in mattresses and chairs which are cased in casing (bags). The casings are successively formed in a pocket form from a sheet of non-woven fabric or cloth.
2. Description of the Prior Art
A conventional type of cased coil spring producing apparatus is not equipped with any hardening device for hardening the coil springs. Thus, it has the problem of the produced coil springs being weak in resiliency and having low durability. To eliminate those problems, an expensive, oil-tempered, wire rod is used in forming the coil springs. However, since the oil-tampered wire rod has a strong resiliency, it takes much time and labor to form the oil-tempered wire rod into a coiled form. Thus, productivity is decreased and manufacturing costs of the coil springs is increased, in addition to the expensive wire rod.
The formed coil springs are put into a compressed state and then are inserted in the casings. In putting the coil springs into the compressed state for insertion, a large-stroke cylinder rod having at its tip end thereof a circular compressing plate has been generally used. The coil springs, after being placed in cylindrical guides to be in a vertical position, are each compressed with the compressing plate from above by a force of the cylinder rod and are then pushed at an outer diameter portion thereof to be inserted in the casing. This conventional method, however, involves the problem of low productivity because the feeding of the next coil spring cannot be done until the compressing plate is raised up.
In addition, since the coil springs thus formed are all the same in resiliency (rigidity), when rows of cased coil springs are linked to form a mat or equivalent, the resultant mat or equivalent cannot have a partially different resiliency.
To solve these problems, the applicant previously proposed a pocket coil spring producing apparatus (US Patent Publication No. 5,740,597, corresponding to the Japanese Laid-open Patent Publication No. Hei 9(1997)-173673). The proposed apparatus has, however, the disadvantage that when the production speed of the pocket coil spring producing apparatus is increased to increase productivity, the coil spring producing mechanism tend to produce errors in cutting of the wire. It also has undesirable tendencies of delays in hardening, conveying, compression, and insertion of the coil springs formed in the coil spring producing mechanism. In addition, mistakes in the process of laying down the coil springs as compressed vertically in the sheet casings or bags to their horizontal position are common.